Regulator device for an asynchronous machine used in particular as a drive for electric vehicles

ABSTRACT

A control apparatus for an asynchronous machine, in particular as a drive for electric vehicles, is equipped with an incremental transducer for the rotation speed of the asynchronous machine and a torque setpoint transducer, the signals of which can be delivered to a setpoint-value entry device in order to generate setpoint values (three-phase reference sine-wave system) for a closed-loop-controlled inverter or inverter power section to operate the asynchronous machine. The setpoint-value entry device contains means for defining at least the rotor frequency (slip frequency) and the amplitude as a function of the desired torque setpoint value. The setpoint-value entry device contains a summing device for adding or subtracting the rotor frequency to or from the mechanical rotation frequency, corresponding to the rotation speed, of the asynchronous machine as a function of the instantaneous rotation direction, the desired rotation direction, and the direction of the desired torque. On the basis of the output signal of the summing device, current setpoint profiles for the inverter or inverter power section, the amplitudes of which can be set as a function of the predefined amplitude, can be selected from a setpoint memory. This control apparatus allows many advantages of the field-oriented control method, and in particular improved efficiency in part-load operation, to be achieved with little outlay and in economical manner. In the particular case of electric vehicles, smooth starting from rest, or from a rolling motion at any speed opposite to the desired direction of motion, is guaranteed.

FIELD OF THE INVENTION

This application is a 371 of PCT/DE97/00123 filed Jan. 22, 1997.

The present invention relates to a control apparatus for an asynchronousmachine, in particular as a drive for electric vehicles.

BACKGROUND INFORMATION

A conventional control apparatus is described in U.S. Pat. No.5,481,168. In this conventional apparatus, the rotation speed of athree-phase induction motor is delivered via an analog/digital converterto a rotation speed measurement device in order to regulate anasynchronous machine. A setpoint transducer predefines a torque, andthese signals are fed into a three-phase system to generate setpointvalues. The sensed rotation speed of the asynchronous machine iscompared to the predefined rotation speed, and the difference isdelivered to the power section of an inverter as the setpoint value.

Another conventional control apparatus of this kind is the so-called"field-oriented" control system as described, for example, in SiemensResearch and Development Reports 1972, F. Blaschke, "The fieldorientation method for controlling asynchronous machines", p. 184 ff.,or in the textbook "Control of Electrical Drives," W. Leonhard,Springer-Verlag, pp. 214-222. With the field-oriented control system,both the amplitude of the stator flux vector and its position withrespect to the rotor flux vector must be monitored at all times. One ofthe principal tasks in this connection is decoupling the torque-basedand flux-based currents from the magnitude of the stator current vector.It is also important to ensure that they are at right angles to oneanother, in a rotor-based coordinate system, at all times. This requiressensing the stator currents of the three-phase system, transforming theminto a coordinate system which rotates synchronously with the rotorflux, and comparing them with the setpoint definitions for theflux-forming component and torque-forming component of the current. Thenew current/voltage values applied to the motor are based on calculationand inverse transformation from the rotating reference system to thesteady-state stator coordinate system. The field-oriented control systemyields a constant torque even above the nominal rotation speed, improvedvelocity consistency even under fluctuating load conditions, and highefficiency at full load, but the technical outlay is high and costly.

SUMMARY OF THE INVENTION

The control apparatus according to the present invention achieves manyof the advantages of the field-oriented control system with technicallysimpler means and in more economical fashion, and achieves betterefficiency particularly in part-load operation, which is principallyrelevant for electric vehicles. The demands on the incrementaltransducer are low. Four-quadrant operation is possible. In addition,smooth starting from rest, or from a rolling motion at any speedopposite to the desired direction of motion, is achieved in outstandingfashion.

The setpoint-value entry device advantageously contains function tablesfor the rotor frequency and the amplitude of the stator current as afunction of the desired torque setpoint. In addition, function tablescan also be provided for the load angle pilot control. The machineparameters are reflected in the values obtained from the functiontables. Each setpoint input is associated with a different value pair orvalue triplet.

In order to take into account the particular rotation direction of theasynchronous machine, the summing device possesses a first switchingdevice which switches over automatically as a function of the particularrotation direction and with which the signals from the incrementaltransducer, that are proportional to the mechanical rotation frequency,are given a negative value in the reverse switch position and a positivevalue in the forward switch position.

In order also to take into account the desired rotation direction andthe direction of the desired torque when defining the setpoint, thesumming device additionally possesses a second switching device whichswitches over as a function of the desired direction of the torque(generator or motor mode): in generator mode, the signals correspondingto the rotor frequency are subtracted from the incremental transducersignals prior to analysis by the first switching device, and in motormode the signals corresponding to the rotor frequency are added to theincremental transducer signals analyzed by the first switching devicewhen the forward rotation direction is predefined, and subtracted fromthem when the reverse rotation direction is predefined. In this manner,the instantaneous rotation direction, the desired rotation direction,and the direction of the desired torque are automatically taken intoaccount in defining the setpoint.

A third switching device controllable by a travel direction switch ispreferably provided for corresponding analysis of the signalscorresponding to the rotor frequency for the forward and reverserotation directions.

To constitute a reference signal from the signals of the incrementaltransducer and the signals corresponding to the rotor frequency, anaccumulator is preferably provided whose inputs are advantageouslyconnected to the outputs of the second and third switching devices.

The setpoints are selected via values determined in the summing devicewhich each constitute an address for a sine-wave table serving as thesetpoint memory. A further improvement can be achieved in that a loadangle correction stage for correcting the address values as a functionof a load angle respectively matching the desired torque, configured inparticular as an adding stage, is provided.

The amplitude of the stator current that is desired or is predefined bythe setpoint input is advantageously established by the fact that amultiplier stage, for multiplying the current setpoint profiles by therespectively predefined amplitude value, is connected downstream fromthe setpoint memory.

The closed-loop-controlled inverter advantageously contains a two-pointcontroller to which three current setpoint profiles, constituted fromthe setpoint profiles at the output of the setpoint memory by way of aconversion stage, are delivered.

BRIEF DESCRIPTION OF THE DRAWING

The FIG. shows a block diagram of a control apparatus for anasynchronous machine according to an exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION

In the exemplary embodiment depicted in the single FIGURE, aclosed-loop-controlled inverter power section 10 controls anasynchronous machine 11 which serves to drive an electric vehicle (notillustrated). Other possible applications of the asynchronous machinemay, of course, also be implemented. Inverter power section 10 containsa two-point hysteresis controller (not depicted in detail) for injectingthe three setpoint currents I_(s1), I_(s2), and I_(s3) into asynchronousmachine 11, these setpoint currents being generated in a setpoint-valueentry device 12. The three actual currents necessary for the controlsystem are sensed in current measurement devices 13-15 in the threesupply leads to asynchronous machine 11, and delivered back to inverterpower section 10. The basis of the modulation principle is that thetwo-point hysteresis controller in inverter power section 10 compares athree-phase reference sine-wave system (setpoint profiles) to the actualcurrents of asynchronous machine 11, thus supplying the appropriateactivation signals for the power switch (not depicted) in inverter powersection 10. This is therefore a current-impressing method. The principaltask of this modulation method is to generate, by way of setpointvalueentry device 12, a reference sine-wave system which is optimum for eachoperating condition of the machine. That makes it possible to define anydesired combination of rotor frequency f₂ (slip frequency) and referencesine-wave system amplitude. The rotor frequency is the frequencyactually "seen" by the rotor of asynchronous machine 11, regardless ofthe instantaneous rotation speed of the rotor. For this, the referencesine-wave system is used to impress onto the stator of the machine afrequency which is greater, by the desired rotor frequency f₂ than thefrequency which would correspond to the mechanical rotation speed. Alsodelivered to inverter power section 10, in a conventional manner, is anintermediate circuit voltage which, in electric vehicles, is the batteryvoltage.

The torque request, from the driver of the electric vehicle or someother operator, for the asynchronous machine contains three dataelements, namely the desired travel direction, the magnitude of thetorque, and the direction of the torque (i.e. motor mode or generatormode). These three data elements are needed to generate the setpointsystem. Information about the rotation speed and direction ofasynchronous machine 11 is also necessary. The rotation speed f_(n) ofasynchronous machine 11 is ascertained using an incremental transducer16 whose signals are delivered to a summing device 17 in setpoint-valueentry device 12. The desired travel direction (forward/reverse) isdefined by way of a travel direction switch 18. The magnitude of thetorque is defined by the driver via an accelerator pedal 19, motor modeof asynchronous machine 11 being present or selected when acceleratorpedal 19 is actuated, and generator mode thereof when the acceleratorpedal is not actuated. A brake pedal (not depicted) is also provided inthe electric vehicle. The pedal positions lead to either a drivesetpoint or a braking setpoint. When both pedals are in the restposition, braking status is established. A vehicle management systemwhich generates the setpoints can also be provided in a conventionalmanner.

The magnitude A of the amplitude of the reference sine-wave system to begenerated, the rotor frequency f₂, and a load angle signal Lw, aregenerated from the magnitude of the preselected torque. For this,accelerator pedal 19 is coupled to a signal generator stage 20 whichgenerates at its output a setpoint signal sw, corresponding to theaccelerator pedal position, for the torque. From this signal sw, theoptimum combination of values f₂ and A pertaining to each setpoint inputis selected from a rotor frequency table 21 and an amplitude frequencytable 22. In addition, the load angle signal Lw can be selected from athird table (not depicted).

The reference sine-wave system to be generated is then approximatedusing i interpolation points. The rotation speed is ascertained byincremental transducer 16 using n signals per revolution, and theasynchronous machine has p pole pairs. The idea is to correct therotation speed and phase of the electrical system to the mechanicalrotary motion of the rotor, thus obtaining a reference sine wave whichinitially is synchronous with the mechanical rotary motion. This isachieved by the fact that each signal of the incremental transducerresults directly in an advance of the phase of the reference sine wavein accordance with its weight. That weight depends on the number ofsignals of the incremental transducer per revolution, and on the numberof motor pole pairs.

In order to obtain a torque, the frequency of this reference sine wavemust be increased or decreased by exactly the rotor frequency f₂matching the particular torque input, as a function of the instantaneousrotation direction, the desired rotation direction, and the direction ofthe desired torque. If these parameters can be varied at will, a fullycapable four-quadrant drive is then implemented. This implementation isattained by way of summing device 17.

In summing device 17, the incremental transducer signals f_(n) areconveyed via a pre-subtraction stage 23 to a first switchover device 24,these signals being delivered to an accumulator in the forward switchposition, and via a sign-changing stage 26 to accumulator 25 in thereverse switch position. The forward/reverse switching signal for firstswitching device 24 is obtained, in a conventional manner from thesignals of incremental transducer 16.

The rotor frequency f₂ is also delivered to a second switchover device27 where in generator mode G it is delivered to a subtraction input ofpre-subtraction stage 23, and in motor mode M it is delivered to a thirdswitchover device 28. The two switch positions (generator mode G andmotor mode M) are predefined as reference variables via acceleratorpedal 19. The two switch positions (forward V and reverse R) of thirdswitchover device 28 are also predefined as reference variables viatravel direction switch 18. In the forward switch setting, the rotorfrequency signals f₂ are delivered directly to accumulator 25, and inthe reverse switch position they are delivered to that accumulator 25via a sign-changing stage 29.

In generator mode, G the weight of the incremental transducer pulsesf_(n) is reduced in pre-subtraction stage 23 in accordance with rotorfrequency f₂. The signals thereby obtained are delivered by firstswitchover device 24, as positive or negative pulses depending onwhether the vehicle is traveling forward or in reverse, to accumulator25, where an addition or subtraction takes place accordingly. In motormode, M the rotor frequency signals f₂ are delivered to the accumulatoras positive or negative signals as a function of whether forward orreverse travel was preselected via third switchover device 28, so thatthe content of accumulator 25 is incremented by the weight of the rotorfrequency in the case of forward travel, and decremented thereby ifreverse travel is desired.

A load angle adding stage 30 in which a load angle value Lw is alsoadded to the accumulator value is connected downstream from accumulator25. This load angle pilot control system once again manipulates thephase of the system; for vehicle drives, it is generally sufficient tokeep the magnitude of the load angle constant, simply ensuring that thedirection always points in the direction of the desired torque. Forhighly dynamic drives, a different load angle magnitude will beassociated with each torque input. For this reason, a load angle addingstage 30 of this embodiment can be omitted from vehicle drives.

The accumulator value corrected by load angle adding stage 30 representsthe address for a downstream sine-wave table 31, in which twostandardized sine-wave signals I_(sn1) and I_(sn2), offset by 120degrees, are constituted. In downstream multiplication stage 32, thesestandardized sine-wave signals are multiplied by the matching amplitudeA of reference sine-wave system I_(s1) and I_(s2) to be generated. Thethird setpoint I_(s3) is easily obtained by way of an adding stage 33and a sign-changing stage 34.

What is claimed is:
 1. A control apparatus for controlling anasynchronous machine, comprising:an incremental transducer determining arotation speed of the asynchronous machine, the incremental transducergenerating incremental transducer signals corresponding to a mechanicalrotational frequency, the mechanical rotational frequency correspondingto the rotation speed and being determined as a function of aninstantaneous rotation direction, a predetermined rotation direction anda predetermined torque direction; a torque setpoint transducergenerating torque output signals; an inverter system having athree-phase reference sine-wave system, the inverter system being one ofa closed-loop-controlled inverter and an inverter power section; and asetpoint-value entry device receiving the torque output signals togenerate setpoint values in the three-phase reference sine-wave systemfor operating the asynchronous machine, the setpoint-value entry deviceincluding:an arrangement defining at least a rotor frequency or a slipfrequency, and a predetermined amplitude, as a function of apredetermined torque setpoint value, a summing device receiving theincremental transducer signals and generating a summing output signal,and a setpoint memory,wherein the setpoint-value entry device selectscurrent setpoint profiles from the setpoint memory for the invertersystem as a function of the summing output signal, the current setpointprofiles having amplitudes which are selected as a function of thepredetermined amplitude.
 2. The control apparatus according to claim 1,wherein the arrangement has function tables to define the rotorfrequency and the predetermined amplitude of a stator current as afunction of the predetermined torque setpoint value.
 3. The controlapparatus according to claim 2, wherein the arrangement includes furthertables to define a load angle pilot control as a function of thepredetermined torque setpoint value.
 4. The control apparatus accordingto claim 1,wherein the summing device includes a first switching devicewhich automatically switches as a function of the instantaneous rotationdirection of the asynchronous machine, and wherein the first switchingdevice generates a negative value in a reverse switch position and apositive value in a forward switch position using the incrementaltransducer signals received from the incremental transducer, theincremental transducer signals being proportional to the mechanicalrotational frequency.
 5. The control apparatus according to claim4,wherein the summing device further includes a second switching devicewhich switches as a function of the predetermined torque direction inone of a generator mode and a motor mode, wherein, in the generatormode, rotor signals corresponding to the rotor frequency are subtractedfrom the incremental transducer signals before the rotor signals areanalyzed by the first switching device, and wherein, in the motor mode,the rotor signals are added to the incremental transducer signals, therotor signals being analyzed by the first switching device when aforward rotation direction is predefined, the rotor signals beingsubtracted from the incremental transducer signals when a reverserotation direction is predefined.
 6. The control apparatus according toclaim 5, further comprising:a travel direction switch, wherein thesumming device further includes a third switching device controllable bythe travel direction switch, the third switching device analyzing therotor signals for the forward and reverse rotation directions.
 7. Thecontrol apparatus according to claim 6, wherein the setpoint-value entrydevice includes an accumulator which generates a reference signal as afunction of the incremental transducer signals and the rotor signals. 8.The control apparatus according to claim 7, wherein outputs of thesecond and third switching devices are connected to inputs of theaccumulator.
 9. The control apparatus according to claim 6, wherein thesetpoint-value entry device includes an accumulator which generates areference signal as a function of the incremental transducer signals andthe rotor signals.
 10. The control apparatus according to claim1,wherein the setpoint memory has a sine-wave table, and wherein thesumming device determines at least one value indicative of at least onecorresponding address in the sine-wave table.
 11. The control apparatusaccording to claim 10, wherein the setpoint-value entry device includesa load angle correction stage which corrects the at least one value as afunction of a load angle to match a predetermined torque.
 12. Thecontrol apparatus according to claim 11, wherein the load anglecorrection stage is an adding stage.
 13. The control apparatus accordingto claim 1,wherein the setpoint-value entry device includes a multiplierstage which multiplies the current setpoint profiles by a value of thepredetermined amplitude, and wherein the multiplier stage is connectedto the setpoint memory downstream from the setpoint memory.
 14. Thecontrol apparatus according to claim 1,wherein the setpoint-value entrydevice includes a stage which generates three current setpoint profiles,and wherein the stage is associated with at least one of the setpointmemory and a multiplier stage.
 15. The control apparatus according toclaim 1, wherein the inverter system includes a two-point controller.16. The control apparatus according to claim 15, wherein the two-pointcontroller is a two-point hysteresis controller.
 17. The controlapparatus according to claim 1, wherein the control apparatus is a drivefor an electric vehicle.